package txyz;

import java.util.Scanner;

public class code01 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        long res  = 1;
        int count = 0;
        for (int i = 1; i <= n; i++) {
            res *= i;
        }
        String s = String.valueOf(res);
        char[] charArray = s.toCharArray();

        for (int i = 0; i < charArray.length; i++) {
            if (charArray[i] == '0') {
                count ++;
            }
        }
        System.out.println(count);

    }
}
